1. Field of the Invention
The present invention relates to a weight plate of a vacuum evaporation apparatus for pressing by gravity so as to prevent displacement between a shadow mask and a glass substrate that are superposed and aligned in a vacuum evaporation apparatus, and to the vacuum evaporation apparatus using the same.
2. Description of the Related Art
In a production process of an organic EL panel that supports full color light emission, red (R), green (G), and blue (B) color elements are formed on a glass substrate by a vacuum evaporation process using a shadow mask.
A method which is widely adopted for forming the color element of each color includes the steps of making shadow masks for individual RGB colors, aligning the shadow mask for each color, and performing vacuum evaporation on the glass substrate.
The shadow mask and the glass substrate are fixed with a holding member and conveyed through a plurality of film forming apparatuses. In the conveying process, the shadow mask and the glass substrate may receive various physical external stresses when using a lifting gear, a roller acceleration/deceleration gear, a belt conveyer, a robot conveyer, and the like. Therefore, their impact force may cause displacement between the shadow mask and the glass substrate, and the positional accuracy thereof may deviate from a target value, thereby resulting in various problems such as color shift, color irregularity, no emission, and the like.
A feature of the production apparatus of an inline production method or the like for the organic EL panel is an improvement of production capacity and reduction of production cost in a continuous mass production form, and it is important how to increase convey speed of the glass substrate so that the production capacity and the operating rate is improved.
In the production apparatus of the inline production method for the organic EL panel, various economic convey mechanisms and units such as a robot conveyer, a roller conveyer, and a belt conveyer are used. When those convey mechanisms are used and intended to increase in convey speed of the substrate, an impact or a vibration occurs due to the acceleration or deceleration.
In addition, the substrate holder is a metal rigid body and has a larger mass than the substrate has. For instance, it is found that a negative acceleration of approximately 1 to 10 m/sec2 is generated at a moment when the moving combined structural member of the shadow mask and the glass substrate including the substrate holder contacts a roller or a conveyer stop portion and is stopped. If the negative acceleration of such an extent is applied to an object having a large mass, impact force of the extent corresponding to a product of the mass and the negative acceleration is exerted, and hence the displacement may occur at a level of 3 to 8 μm. On the other hand, the substrate is usually a thin glass plate having a thickness of 1 mm or less and has a small mass. Therefore, the impact force is small for the substrate even if the same negative acceleration is exerted. A difference of the impact forces applied to the substrate holder and the substrate may cause a displacement.
A substrate holder that may solve such problem is disclosed in Japanese Patent Application Laid-Open No. 2007-046099. As illustrated in FIG. 15, the substrate holder includes a mask holder 5 for holding a shadow mask 6, which is provided with a friction pad 2, and a substrate holder 3 for holding a substrate 4, which is provided with a friction pad 17. The friction pad 2 and the friction pad 17 are disposed at positions so as to contact each other and are made of rubber or elastomer.
Thus, the friction force between a fringe part of clamping the mask holder 5 and the substrate holder 3 with a clamper 7 so as to hold the shadow mask 6 and a fringe part of holding the substrate 4 is increased, to thereby prevent a relative displacement between the shadow mask and the glass substrate.
Furthermore, the shadow mask is fixed to the mask holder 5 by magnetic attractive force using a magnet or the like.
However, magnetic force may cause an image disturbance in the production process of the organic EL panel. In particular, it is said that if a stripe mask is used, magnetic lines of flux are generated so that a distance between the stripe masks varies, resulting in an image disturbance due to a displacement of a film forming position of an organic light emission film.